1. Field of the Invention
The invention generally relates to a method and apparatus for substrate process monitoring.
2. Background of the Related Art
Semiconductor processing generally involves the deposition and removal (“etching”) of materials, such as conductors, semi-conductors, and insulators, onto or from substrates to form integrated circuits and other electronic devices. Typical processes include chemical vapor deposition (CVD), physical vapor deposition (PVD), electroplating, chemical mechanical planarization (CMP), etching, and others.
During the processing and handling of substrates, the substrates undergo various structural and chemical changes. Unfortunately, some changes result in contamination, such as the formation of unwanted oxide layers from the reaction of a metallic layer with oxygen. In order to achieve proper device performance, it is important that each layer of material is deposited on, or removed therefrom, a surface substantially free of contamination. For example, failure to provide clean device interconnects having features such as contacts, vias, trenches, and the like, free of contamination, can cause faulty connections and/or increase the resistance of the features, degrading device performance.
One method to clean the surface of a substrate of contamination is a pre-clean process. For pre-clean processing, substrates within a chamber are exposed to a process that cleans the substrate surface of the unwanted impurities such as copper oxides, aluminum oxides, tantalum oxides, and tungsten oxides, and the like, before the next deposition process. One example of a pre-clean process is a reactive pre-clean process used to reduce contamination before the deposition of a subsequent layer of metallization. As one example, a substrate surface contaminated with a copper oxide (CuO) contaminate can be cleaned by exposing the contaminated surface of the substrate to plasma containing hydrogen molecules and helium atoms to chemically reduce the copper oxide contaminate. One method to form the plasma is to flow at least one process gas containing hydrogen and/or helium into a chamber, while maintaining the gas under a desired pressure, and exciting the gas with a power source such as an RF generator using electrodes within the chamber. The plasma dissociates the hydrogen molecules into ions and radicals. The hydrogen ions and radicals diffuse to the contaminated substrate surface where the copper oxide reduction takes place. The reduction of the copper oxide contaminates forms bi-products of water and metallic copper. Generally, the water is removed by the pre-clean processing system through a vacuum pump system adapted to remove water.
One conventional method to ensure that the process is operating within normal parameters requires the periodic insertion of one or more test substrates having a controlled amount of contaminates, such as copper oxides, into the pre-clean chamber for cleaning and analysis. Once cleaned, the test substrates are inspected using external inspection systems. If the test substrates are cleaned within acceptable limits, the chamber is deemed suitable for the pre-clean process.
Unfortunately, production flow is effectively disrupted during the transfer, processing, and external inspection of the test substrates. Consequently, conventional external substrate inspection systems may drastically increase overhead time associated with chip manufacturing. Further, the process may degrade to an unacceptable level before the next inspection, that may allow contaminated substrates to be incompletely processed, resulting in fabrication of defective devices. Still further, contamination problems are compounded in cases where the substrates are re-distributed from a given batch making it difficult to trace back to the contaminating source. Another disadvantage with conventional external substrate inspection systems is the prohibitive cost of the systems. Conventional external substrate inspection systems are typically expensive stand-alone platforms that occupy clean-room space. Because of the large area, or “footprint”, required by the stand-alone inspection platforms, the cost of owning and operating such systems is high. A preferred processing system would include an integrated, or embedded, device capable of continuously monitoring the status of the process and facilitate automatic corrective action. Thus, the processing system could be further integrated and throughput can be increased.
Therefore, there is a need for an integrated in situ substrate inspection system capable of monitoring substrate pre-clean processing and determining one or more conditions of the processing in order to detect process anomalies, endpoints, and facilitate a subsequent pre-clean chamber calibration and/or repair decision.